The present invention relates to the packaging of semiconductor devices. More particularly, the present invention relates to a packaged semiconductor device and a method for making it.
Semiconductor device packaging techniques are well known. In conventional packaged devices, a die is attached to a substrate, and contacts of each are electrically connected. A heat sink may also be affixed to the die. The die and heat sink are then completely encapsulated, using an overmold (a heated container with a cavity), with a mold material. An example of such a conventional packaged device may be found in U.S. Pat. No. 5,901,041 (Davies et al).
Other conventional methodologies include packaging the die and then adding the heat sink, leaving it exposed. Yet other conventional approaches include taping a heat sink to internal leads of the die and encapsulating the die and heat sink.
Referring now to FIGS. 1 and 2, there is shown a conventional packaged semiconductor die assembly 10 including a substrate 22, a die 12, a heat sink 40, and a package molding 50. The substrate 22 has a first surface 24 and a second surface 26. An opening 28 extends between the surfaces 24, 26.
The die 12 has a first surface 14, a second surface 16, and one or more sides 18. The second surface 16 abuts the first surface 24 of the substrate 22. Electrical contacts 20 are located on the second surface 16 and are connected to electrical contacts 30 on the second surface 26 of the substrate 22. The contacts 20, 30 arc connected by wiring 32 which may be printed or bonded.
The heat sink 40 has a first surface 42, a second surface 44, and one or more sides 46. The second surface 44 abuts the first surface 14 of the die 12. The package molding 50 completely encapsulates the die 12 and the heat sink 40. Specifically, the sides 18, 46 and the first surface 42 are covered by the package molding 50.
One problem with such conventional methodologies is that current overmold techniques generally completely encapsulate the head sink with no surface of the heat sink directly exposed as shown in FIG. 2. This reduces efficiency of the heat transfer process.
There thus exists a need for a packaged semiconductor device having a heat sink which allows greater heat transfer properties, particularly as the density of components within a die increases and heat build up becomes more of a problem.
The present invention provides a packaged semiconductor device which includes a substrate, a die connected to said substrate, a heat sink affixed to said die, and a first molding material encapsulating said die and said heat sink, said first molding material leaving exposed substantially an entire upper surface of the said heat sink.
The present invention further provides a molded packaged semiconductor device including a die having first contacts, a substrate connected to the die and having second contacts, the first contacts being connected to respective second contacts, a heat sink, a thermally compliant material adhering the heat sink with the die, and a molding material encapsulating the die, the thermally compliant material, and the substrate, the molding material leaving exposed substantially the entire upper surface of the heat sink.
The present invention further provides a method for packaging a semiconductor device. The method includes affixing a heat sink to a die located on a substrate, and encapsulating the die and the heat sink with a first molding material such that substantially an entire upper surface of the heat sink remains exposed.